The present invention relates to a plasma processing method and a semiconductor device.
There are plasma processing methods that have been proposed in the prior art through which film formation processing is implemented on a target object such as a semiconductor wafer (hereafter referred to as a xe2x80x9cwaferxe2x80x9d). In one such method, for instance, after mounting a wafer on a lower electrode provided within an airtight processing chamber, the wafer is heated to a specific temperature. Then, a processing gas such as SiH4 (silane), TEOS (tetra-ethoxy silane) or the like is introduced into the processing chamber while maintaining the atmosphere within the processing chamber at a specific reduced pressure. Next, high frequency power for plasma generation is applied to an upper electrode facing the lower electrode and high frequency power for biasing is applied to the lower electrode, to generate plasma by dissociating the processing gas. In the next step, a layer insulating film constituted of SiO2 (silicon dioxide) is formed on the Si (silicon) substrate constituting the wafer, using the plasma.
The adoption of a multilayer wiring structure on an Si substrate achieved by laminating wiring films over a plurality of layers via layer insulating film has become essential to support ultra-fine semiconductor elements of various types formed at the wafer and the ultra-high integration that have been achieved in recent years. In addition, with the design rules for designing semiconductor devices becoming further reduced, the wiring films are positioned in closer proximity to each other and the layer insulating film is becoming even thinner. However, if an SiO2 film having a dielectric constant of approximately 3.9 is utilized to constitute the layer insulating film, as in the prior art, the capacity between the wirings (incidental capacity) increases and, as a result, the transmission of electrical signals is delayed to result in a reduction in the high-speed operability. Consequently, it is difficult to drive at a low voltage, and moreover, it is difficult to operate at a high clock frequency.
As a solution, a method of lowering the capacity between the wirings by employing a film with a low dielectric constant which has a dielectric constant lower than that of SiO2 to constitute the layer insulating film has been proposed. The film with a low dielectric constant employed in such a method may be a film constituted of an organic material or a film constituted of an inorganic material. The dielectric constants of a polyimide resin film and a fluorine-containing resin film, either of which may constitute the organic film are 3.0xcx9c3.5 and 1.9xcx9c2.7 respectively, and are much lower than that of the SiO2 film. However, organic films do not possess a significant degree of heat resistance due to their poor strength in their molecular structures, and they do not facilitate machining either. In addition, the conformability of organic films to the existing processing methods is poor, which makes it difficult to form various types of elements.
In contrast, an inorganic film such as an SiOF (silicon oxide containing fluorine) film having a dielectric constant of approximately 3.5 has a relatively stable molecular structure, and therefore, unlike the organic films described above, achieves advantages including superior heat resistance, good machinability and good conformability to existing processing methods. In addition, the SiOF film may be processed using an existing film formation apparatus through an existing film formation method by using a mixed gas constituting of, for instance, SiH4 and SiF4 for the processing gas. Furthermore, since the dielectric constant of the SiOF film has dependency on the content of the F (fluorine) atoms in the film, the dielectric constant can be reduced by increasing the content of the F atoms.
However, when the F atom content in the SiOF film is increased, the hygroscopicity of the film itself becomes higher in proportion to the increase. According to the observation made by the inventors, this increase in the hygroscopicity may be attributable to the following factor. Namely, the SiO2 film has a molecular structure expressed as; 
with an xe2x80x94OH (hydroxyl group) bond at its trailing end. When F atoms are added into the SiO2 film at a quantity at which no hygroscopicity manifests, e.g., at 10 mol % xcx9c20 mol %, to set the dielectric constant to approximately 3.5, the xe2x80x94OH is replaced by xe2x80x94F, and the molecular structure expressed as; 
is achieved. In addition, if F atoms are added into the SiOF film at a ratio exceeding 20 mol % to further reduce the dielectric constant of the SiOF film, the molecular structure changes to 
with the O (oxygen) atom that has been bonded to the two Si atoms replaced by F atoms, thereby destroying the network structure of the SiO2 film. It is assumed that the resulting series of reactions, whereby a reaction occurs between the Si (xe2x80x94F)2 bond formed within the SiOF film and H2O (water) present in the atmosphere and the like to induce hydrolysis and an Sixe2x80x94OH bond is formed, raises the hygroscopicity of the SiOF film.
In addition, when the SiOF film absorbs moisture, HF (hydrogen fluoride) is created, which corrodes any metal in contact with the layer insulating film, such as that constituting the wiring films, to damage the element. Furthermore, if HF becomes diffused inside the processing chamber, it contaminates the processing chamber and may also cause corrosion of various members and the exhaust system provided inside the processing chamber. Moreover, HF reduces the pH (approximately 9xcx9c11) of the slurry used as a polishing agent when flattening the layer insulating film through CMP (chemical mechanical polishing), which results in a reduction in the polishing speed.
A first object of the present invention which has been completed by addressing the problems of the prior art discussed above is to provide a new and improved plasma processing method and a new and improved semiconductor device, which make it possible to form an SiOF film having a low dielectric constant that demonstrates no substantial hygroscopicity.
In addition, in the prior art, if the SiO2 film is in contact with a metal such as Ti (titanium), the Ti and the O in the SiO2 become bonded at the interface to result in the formation of a bridge structure such as xe2x80x94Tixe2x80x94Oxe2x80x94Sixe2x80x94 and, as a result, a specific bond strength is achieved. However, if F is present in the SiO2 film during this process, the bond of the xe2x80x94Tixe2x80x94Oxe2x80x94Sixe2x80x94 is broken into xe2x80x94Tixe2x80x94F, Hxe2x80x94Oxe2x80x94Si and the like, which presents a problem in that the bond with the metal such as that constituting the wiring films in contact with the SiOF film is weakened.
A second object of the present invention which has been completed by addressing the problem of the prior art discussed above is to provide a new and improved plasma processing method and a new and improved semiconductor device, which make it possible to form an SiOB (silicon oxide containing boron) film having a low dielectric constant that achieves a strong bond with the metal material.
In order to achieve the objects described above, in a first aspect of the present invention, a plasma processing method for implementing film formation processing on a target object placed within a processing chamber by transforming a processing gas introduced into the processing chamber into plasma, that includes a step in which a gas that is constituted of, at least, a gas containing silicon atoms, a gas containing oxygen atoms, a gas containing boron atoms and a gas containing fluorine atoms is introduced as the processing gas into the processing chamber and film constituted of a silicon oxide-type material is formed at the target object by incorporating at least the boron atoms and the fluorine atoms into the molecular structure, is provided.
In this method, by introducing the B atoms into the network structure of the Sixe2x80x94O bond in the SiO2 film, for instance, a Bxe2x80x94O bond network is formed within the network constituted of the Sixe2x80x94O bond. Since the B atom is relatively small compared to the Si atom, the O atom and the F atom, the degree of electronic polarization is reduced in the Bxe2x80x94O bond formed within the silicon oxide-type film. As a result, the dielectric constant of the film can be lowered. In addition, by adding the F atoms, the Bxe2x80x94OH bond within the film is replaced by a Bxe2x80x94F bond to achieve a reduction in Bxe2x80x94OH bonds that would otherwise cause hygroscopicity. Since an Si (xe2x80x94F)2 bond having a degree of hygroscopicity is formed if the F atoms are added in an excessively large quantity during this process, the quantity of the F atoms to be added is set within a range of, for instance, 2% xcx9c4% in terms of the number of Sixe2x80x94F bonds/number of Sixe2x80x94O bonds.
In addition, the dielectric constant of the SiOB film with F atoms added is reduced through an increase in B atoms instead of through an increase in F atoms, which is the case in an SiOF film. Consequently, a dielectric constant comparable to that of the organic film mentioned earlier can be achieved by increasing the quantity of B atoms that are added without having to increase the quantity of F atoms, which would damage the Sixe2x80x94O bond network structure and reduce the bond strength with a metal, as explained above. Furthermore, since an SiO2 film, for instance, is formed at the target object by incorporating at least B atoms and F atoms into the molecular structure during the process of film formation, the B atoms and the F atoms are distributed evenly within the SiOB film containing F.
Moreover, by setting the quantity of boron atoms in the processing gas equal to or lower than 50% of the quantity of silicon atoms in the processing gas, a stable SiO2 film achieving a high degree of reliability can be formed.
In addition, by implementing a step in which a gas that contains at least carbon atoms is caused to react with the boron atoms and the fluorine atoms constituting the surface of the silicon oxide film following the step in which the silicon oxide film is formed, SiC (silicon carbide) and BC (boron carbide) that do not react with H2O readily can be formed at the surface. As a result, the hygroscopicity of the exposed surface of the SiOB film containing F, in particular, that is exposed to the atmosphere and therefore, would absorb moisture readily, can be reduced. Furthermore, since the SiC and the BC mentioned above achieve a strong bond with the metal constituting the wiring film and the like, an element having an ultra high density can be formed.
As an alternative, a step in which a gas containing at least nitrogen atoms may be caused to react with the boron atoms and the fluorene atoms constituting the surface of the silicon oxide film may be implemented after the silicon oxide film is formed, to form SiN (silicon nitride) and BN (boron nitride) that also achieves a good bond strength when bonding with a metal without readily absorbing moisture.
Alternatively, after the step in which the silicon oxide film is formed, a step in which a gas containing at least hydrogen atoms is caused to react with the boron atoms and the fluorine atoms constituting the surface of the silicon oxide film may be implemented. By employing this method, the film surface can be terminated with a Bxe2x80x94H bond or an Sixe2x80x94H bond, which makes it possible to form a film having a low dielectric constant that does not absorb moisture readily and achieves a strong bond with metal.
In addition, by implementing a step in which a gas containing at least carbon atoms is caused to react with the boron atoms and the fluorine atoms constituting the surface of the silicon oxide film after the step in which a reaction is caused with the gas containing hydrogen, the Sixe2x80x94C bond and the Bxe2x80x94C bond mentioned earlier can be formed even more easily, so that a film having a low dielectric constant that does not absorb moisture readily and achieves good adhesion with metal is formed.
Furthermore, by implementing a step in which a gas containing at least nitrogen atoms is caused to react with the boron atoms and the fluorine atoms constituting the surface of the silicon oxide film after the step in which a reaction is caused with the gas containing hydrogen, the Sixe2x80x94N bond and the Bxe2x80x94N bond described above can be formed even more easily, to reduce the degree of hygroscopicity and improve the adhesion with the metal.
In a second aspect of the present invention, a semiconductor device that includes an insulating film constituted of a silicon oxide material achieved by incorporating at least boron atoms and fluorine atoms into its molecular structure is provided.
In this structure, which utilizes an SiOB film constituted by incorporating F atoms into the molecular skeleton as the insulating film, the network structure of the Sixe2x80x94O bond can be maintained, the degree of anti-hygroscopicity can be improved through the addition of F atoms and the dielectric constant can be lowered.
In addition, by setting the quantity of boron atoms within the insulating film fundamentally equal to or less than 50% of the quantity of silicon atoms in the insulating film, a stable insulating film achieving a high degree of reliability can be formed, as has been explained in reference to the invention defined in claim 2.
Furthermore, by setting the ratio (Sixe2x80x94F/Sixe2x80x94O) of the number of bonds (Sixe2x80x94F) between silicon atoms and fluorine atoms and the number of bonds (Sixe2x80x94O) between silicon atoms and oxygen atoms to 2% xcx9c4%, as in the invention defined in claim 10, for instance, the formation of the Sixe2x80x94OH bond and the Hxe2x80x94OH bond in the insulating film is prevented, so that even when the film is exposed to the atmosphere, the film is prevented from absorbing moisture.